1. Field of the Invention
The present invention relates generally to a metering device and more specifically to a metering device which features a rotatable metering element.
2. Description of the Related Art
PCT Publication WO 90.backslash.10198 discloses a metering device which features a linearly movable metering head which is reciprocatively disposed within an elongated rotatable member. This device suffers from sealing problems, and, due to its linear design, is relatively bulky for some applications. U.S. Pat. No. 4,058,240 to Becker discloses an automatic drain for a compressed air system which uses a rotating ball. However, this arrangement suffers from the drawback that the ball has no through bore and therefore the amount of gas which can be vented per rotation is limited.
U.S. Pat. No. 3,387,748 to Brenchley discloses a motor driven metering valve wherein a free piston is reciprocatively disposed in a bore formed in a ball-shaped valve member. This free piston is provided with sealing rings and is retained within the bore by retaining rings. However, this arrangement suffers from the drawback that the sealing rings, with the passing of time, a) tend to trap particles and thus invite possible malfunction, and b) wear down and tend to lose their sealing properties. This latter problem allows a leak path to be established permitting fluid to escape past the piston and therefore reduce the precision with this the fluid can be metered.
U.S. Pat. No. 3,037,738 to Jackson et al. discloses a manually operated rotary valve which is not equipped with a metering arrangement. Adjustable valve seats are provided at the upstream and downstream ends of the valve.